SK288290B6 - Vector for expression of heterologous proteins in bacterial host cell, bacterial host cell and process for production of desired heterologous polypeptide - Google Patents

Abstract

The invention relates to avector for the expression of heterologous proteins in a bacterial host cell, comprising at least one expression control sequence, and a nucleic acid molecule coding for a fusion protein, wherein the fusion protein comprises a first polypeptide which is the autoprotease Npro of a pestivirus, or a derivate thereof relating the Npro autoproteolytic activity, and includes a second polypeptide which is a heterologous polypeptide. The invention described a bacterial host cell and a process for the production of a desired heterologous polypeptide with clearly defined homogenous N-terminus in a bacterial host cells.

Description

The present invention relates to a vector for expression of heterologous proteins in bacterial host cells, bacterial host cells and a method for production of a desired heterologous polypeptide with a clearly defined homogeneous N-terminus in a bacterial host cell, wherein the heterologous polypeptide is autoproteolytically cleaved autoproteolytic activity of N ^pro from initially expressed fusion a protein comprising a peptide having an autoproteolytic activity of an autoprotease N ^for pestivirus and a heterologous polypeptide.

BACKGROUND OF THE INVENTION

In the preparation of recombinant proteins in heterologous organisms such as e.g. when expressing human or other eukaryotic proteins in bacterial cells, it is often difficult to obtain a clearly defined N-terminus whose homogeneity is as close as possible to 100%. This applies in particular to recombinant pharmaceutical proteins whose amino acid sequence should in many cases be identical to the amino acid sequence of proteins naturally occurring in human / animal.

For normal, natural expression, e.g. in humans, many pharmaceutical proteins that are used are transported into the extracellular space, and cleavage of the signal sequence present in the precursor protein for this purpose results in a clearly defined N-terminus. Such a homogeneous N-terminus is not always easy to prepare, e.g. in bacterial cell expression, for several reasons.

Only in exceptional cases is export to the bacterial periplasmic space via a prokaryotic or eukaryotic signal sequence appropriate since only a very small amount of product can accumulate due to the low transport capacity of the bacterial export mechanism.

However, bacterial cytoplasm differs significantly from the extracellular space of eukarytic organisms. On the one hand, there are m reducing conditions, on the other hand, there is no mechanism for cleaving the N-terminal leader sequence from the mature protein. The synthesis of all cytoplasmic proteins starts with methionine, which is encoded by the appropriate initiation (start) codon (ATG = translation initiation). This N-terminal methionine is retained in many proteins, while in others it is cleaved by methionine nopeptidase (MAP), which is present in the cytoplasm and is intrinsic to the host. The cleavage efficiency depends essentially on two parameters:

1. the nature of the following amino acid a

2. localization of the N-terminus in the three-dimensional structure of the protein.

The N-terminal methionine is preferably removed when the next amino acid is serine, alanine, glycine, methionine or valine and when the N-terminal is exposed, i. when it is not hidden inside the protein. On the other hand, when the following amino acid is another, especially a charged amino acid (glutamic acid, aspartic acid, lysine, arginine), or when the N-terminus is located inside a protein, in most cases the N-terminal methionine is not cleaved (Knippers, Rolf ( 1995) Molecular Genetics, 6th edition, Georg Thieme Verlag, Stuttgart, New York, ISBN 3-13-103916-7).

Even if the cleavage-promoting amino acid is present at position 2, cleavage is rarely complete. Usually not insignificant amounts (1-50%) remain unaffected with MAP.

In the early days of recombinant pharmaceutical protein production in bacterial cells, the ATG start codon encoding methionine was simply inserted before the open reading frame (ORF) for the mature protein (ie, without a signal sequence or other N-terminal extension). The expressed protein then had the sequence H ₂ N-Met-target protein. Only in a few cases was it possible to achieve complete cleavage of the non-terminal methionine MAP of the host. Thus, most of the proteins produced in this way were either non-homogeneous at their N-terminus (a mixture of the Met-form and a non-Met form), or all molecules had an additional foreign amino acid (Met) at their N-terminus (Met-form only).

However, this inhomogeneity or deviation from the natural sequence is unacceptable in many cases since such products often exhibit different immunological (e.g., antibody induction) and pharmacological properties (half-life, pharmacokinetics). For these reasons, it is now mostly necessary to produce natural identical products (homogeneous and without the foreign amino acid at the N-terminus). In the case of cytoplasmic expression, the remedy is typically a fusion of a leader sequence for a specific endopeptidase (e.g., factor Xa, enterokinase, KEX endopeptidase, IgA protease) or an aminopeptidase (e.g., dipeptidylaminopeptidase) to the N-terminus of the target protein. However, this represents a further step with additional costs and material in downstream processing of the product.

Thus, there is a continuing need for new methods for preparing a target protein in bacterial cells, whereby a target protein with the desired uniform N-terminus would be prepared without the need for additional in vitro steps (refolding, purification, protease digestion, re-purification, etc.). It is also a method using viral autoprotease N ^pro from pestivirus that is the subject of the present invention.

Pestiviruses are a group of pathogens that cause significant economic losses in pig and ruminant farms around the world. A particularly important pathogen is the classical swine fever virus (CSFV), which causes a communicable disease and is therefore subject to a reporting obligation. The losses caused by bovine viral diarrhoea virus diarrhea virus (BVDV) are also significant, mainly due to the regular occurrence of intrauterine fetal infection.

Pestiviruses are small envelope viruses whose genome of 12.3 kb acts directly as an mRNA from which viral products are transcribed in the cytoplasm. This occurs in the form of a single polyprotein that contains approximately 4000 amino acids and that is cleaved by viral and cellular proteases into 12 mature proteins.

To date, two proteases encoded by the virus have been identified in pestiviruses, the autoprotease N ^pro and the serine protease NS3. The N-terminal protease N ^pro is located at the N-terminus of the polyprotein and has an apparent molecular weight of 23,000 (D). It catalyzes the cleavage that occurs between its own C-terminus (Cysl68) and the N-terminus (Ser169) of the nucleocapsid protein C (R. Stark et al., J. Virol. 67 (1993), 7088-7095). In addition, duplications of the N ^pro gene have been described for cytopathogenic BVDV viruses. There is a second copy of N ^pro at the N-terminus of a similarly duplicated NS3 protease. Autoproteolytic cleavage of protein N ^for NS3 was also observed in this case (R. Stark et al., Supra).

N ^pro is an auto-protease of 168 amino acids (aa) in length and an apparent M _{r of} 20,000 (D) (in vivo). It is the first protein in a pestivirus polyprotein (such as CSFV, BVDV or BDV (border disease virus)) and undergoes autoproteolytic cleavage from the following nucleocapsid protein C (M. Wiskerchen et al., J. Virol. 65 (1991), 4508-). Stark et al., J. Virol 67 (1993), 7088-7095). This cleavage is performed after the last amino acid of the N ^pro sequence, ie Cys 168.

SUMMARY OF THE INVENTION

It has now surprisingly been found that the autoproteolytic function of the autoprotease N ^for pestivirus is maintained in the bacterial expression system, particularly in the expression of heterologous proteins. Thus, the present invention relates to a method for producing a heterologous polypeptide of interest with a clearly defined N-terminus in a bacterial host cell, wherein the heterologous polypeptide of interest is an autoproteolytic activity of N ^for cleaved from a fusion protein initially expressed comprising a peptide with autoproteolytic activity of autoprotease N ^for pestivirus. polypeptide. The present invention further relates to cloning means used in the methods of the invention.

Preferably, the polypeptide having the autoproteolytic activity of the autoprotease N ^for pestivirus or the polypeptide with the autoproteolytic function of the autoprotease N ^for pestivirus is preferably the autoprotease N ^for pestivirus or a derivative thereof with autoproteolytic activity.

In the present invention, the term heterologous polypeptide means a polypeptide that is not naturally cleaved by autoprotease N ^for pestivirus from a naturally occurring fusion protein or polyprotein. Examples of heterologous polypeptides include enzymes or polypeptides with pharmaceutical activity, particularly human pharmaceutical activity.

Examples of preferred polypeptides with human pharmaceutical activity include cytokines such as interleukins, e.g. IL-6, interferons such as leukocyte interferons, e.g. interferon a2B, growth factors, especially growth factors involved in hematopoiesis or wound healing, such as e.g. G-CSF, erythropoietin or IGF, hormones such as e.g. human growth hormone (hGH), antibodies or vaccines.

One aspect of the invention relates to a nucleic acid encoding a fusion protein, said fusion protein comprising a first polypeptide which has the autoproteolytic activity of an autoprotease N ^pro of pestivirus, and a second polypeptide which is connected to the first polypeptide at the C-terminus of the first polypeptide so as wherein the second polypeptide can be cleaved from the fusion protein by the autoproteolytic activity of the first polypeptide, wherein the second polypeptide is a heterologous polypeptide.

The pestivirus is preferably selected from the group consisting of CSFV, BDV and BVDV for the purposes of the invention, particularly preferred is CSFV.

A preferred nucleic acid of the invention is a molecule, wherein the first polypeptide of the fusion protein comprises the amino acid sequence of the autoprotease N ^pro of CSFV (see also sequence accession number X87939 in the EMBL) (amino acids 1 to 168, reading in N-terminal to the C-terminus).

(L) -MELNHFELLYKTSKQKPVGVEEPVYDTAGRPLFGNPSEVHPQSTLKLPHDRGRGDIRTTL RDLPRKGDCRSGNHLGPVSGIYIKPGPVYYQDYTGPVYHRAPLEFFDEAQFCEVTKRIGRVTGS DGKLYHIYVC VDGCILLKLAKRGTPRTLKWIRNFTNCPLWVTSC- (168), or the amino acid sequence of a derivative thereof having the autoproteolytic activity.

Derivatives with the autoproteolytic activity of the autoprotease N ^for pestivirus are autoproteases N ^for prepared by mutagenesis, in particular using substitutions, deletions, additions and / or amino acid insertions, while maintaining the desired autoproteolytic activity, especially to generate the desired proteins with a homogeneous N-terminus. Methods for preparing such derivatives by mutagenesis are known to those skilled in the art. By such mutations it is possible to optimize the activity of autoprotease N ^pro , e.g. in relation to the various heterologous proteins to be cleaved. After the preparation of a nucleic acid that encodes a fusion protein that, in addition to the heterologous protein of interest, contains an autoprotease N derivative ^for one or more mutations relative to autoprotease N ^for occurring in nature, it is determined whether the desired function is present by determining autoproteolytic activity in the expression system.

The autoproteolytic activity may be e.g. initially detected in the in vitro system. For this purpose, the DNA construct is transcribed into RNA, and then translated into protein using an in vitro translation kit. To increase sensitivity, the resulting protein may in some cases be labeled with incorporation of radioactive amino acids. The resulting fusion protein N ^pro -target protein is subjected to cotranslational and / or posttranslational autocatalytic cleavage when precise cleavage of the N-terminal N ^{for the} region from the remainder of the protein by its own autoproteolytic activity occurs. The resulting cleavage products can be easily detected and the mixture can be easily processed immediately after the in vitro translation is complete. The mixture is loaded onto a protein analysis gel (Lämmli SDS-PAGE) and subjected to electrophoresis. The gel is then stained with suitable dyes or autoradiography is performed. Western blot analysis followed by immunostaining is also possible. Cleavage efficiency of the fusion protein can be evaluated based on the intensity of the resulting protein bands.

In a next step, the nucleic acid fragment for the fusion protein can be cloned into a bacterial expression vector (unless this has already been done for in vitro translation) and is then transformed into a suitable host (e.g., E. coli). The resulting expression strain expresses the fusion protein either constitutively or upon addition of an inducer. If an inducer is used, the host must be further cultured for 1 hour to several hours after addition of the inducer to obtain a sufficient product titer. N ^{for the} auto-protease then cleaves itself the co- or post-translational fusion protein so that the resulting fragmentary ones are N ^for auto-protease alone and the target protein itself with a defined N-terminus. To determine the efficiency of the cleavage reaction, a sample is analyzed by SDS-PAGE at the end of the culture or induction phase as described above.

A preferred autoprotease N derivative ^{for the} disclosed fusion protein has e.g. An N-terminal region wherein one or several amino acids have been deleted or substituted in the amino acid region 2 to 21, as long as the resulting derivative continues to exhibit the autoproteolytic function of autoprotease N ^pro to the desired extent. A preferred autoprotease N ^pro derivative in the fusion protein comprises e.g. the amino acid sequence of autoprotease N ^pro from CSFV with amino acid deletions of 2 to 16 or 2 to 21. It is also possible to alter or insert an amino acid sequence, e.g. an amino acid sequence is introduced that facilitates purification (see Examples).

A particularly preferred nucleic acid molecule of the invention is one wherein the first polypeptide comprises the amino acid sequence Glu22 to Cysl68 of autoprotease N ^pro from CSFV or a derivative thereof with autoproteolytic activity, wherein the first polypeptide additionally has Met as the N-terminus and the heterologous polypeptide is linked directly to the amino acid Cysl68 autoprotease N ^pro of CSFV.

Similarly, a preferred nucleic acid molecule of the invention is one wherein the first polypeptide comprises the amino acid sequence Prol7 to Cys186 of autoprotease N ^pro from CSFV or a derivative thereof with autoproteolytic activity, wherein the first polypeptide additionally has Met as the N-terminus and the heterologous polypeptide is linked directly to the amino acid Cysl68 autoprotease N ^pro of CSFV.

The nucleic acid molecule of the invention is preferably in the form of a DNA molecule.

The present invention further relates to cloning elements, in particular expression vectors and host cells, which comprise the nucleic acid molecule of the present invention. The invention further relates to an expression vector which is compatible with a pre-defined bacterial host cell and which comprises at least one expression control sequence. The expression control sequences are primarily promoters (e.g., lac, tac, T3, T7, trp, gac, vhb, lambda pL or phoA), ribosome binding sites (e.g., natural ribosome binding sites belonging to the aforementioned promoters, cro or synthetic binding sites). ribosome sites) or transcription terminators (e.g., rrnB T1T2 or bla). The host cells are preferably bacterial cells of the genus Escherichia, in particular E. coli. However, other bacterial cells may also be used. In a preferred embodiment of the invention, the expression vector of the invention is a plasmid. The present invention further relates to a bacterial host cell comprising an expression vector of the invention. Such bacterial host cells may be selected from the group consisting of the following microorganisms: gram-negative bacteria of the genus Escherichia, especially E. coli or other gram-negative bacteria, e.g. Pseudomonas sp., Such as e.g. Pseudomonas aeruginosa, or Caulobacter sp., E.g. Caulobacter crescentus, or gram-positive bacteria such as bacillus sp., Especially Bacillus subtilis. Particularly preferred host cells are E. coli.

The present invention further relates to a method for producing a desired heterologous polypeptide, comprising the steps of:

(i) culturing bacterial host cells of the invention comprising an expression vector of the invention comprising a nucleic acid molecule of the invention, wherein the cultivation takes place under conditions that cause expression of the fusion protein and further autoproteolytic cleavage of the heterologous polypeptide from the fusion protein in the host cell by autoproteolytic activity and (ii) isolating the cleaved heterologous polypeptide.

The method of the invention is carried out in principle by the initial cultivation of bacterial host cells, i. j. an expression strain of these cells, in a conventional microbiological manner known to those skilled in the art. The strain is cultured from a single colony on nutrient medium, but it is also possible to use a cryopreserved cell suspension (cell banks) as a starting material. The strain is generally cultured in a multi-step process to obtain sufficient biomass for further processing.

Small scale cultivation is performed in shake culture flasks, in most cases a complete medium (e.g. LB nutrient medium) can be used. However, a specifically defined medium (e.g. citrate medium) may also be used. For culture, a small-scale precursor culture of the host strain (inoculated with a single colony or cryopreserved cell suspension) is prepared, the temperature of this culture usually not critical for later expression results, so that it is routinely performed at higher temperatures (e.g. 30 ° C or 37 ° C). The main culture is seeded in a larger volume (eg 500 ml) where good aeration is required (large volume of flask vs. volume, high rotation speed). Due to the intention to achieve expression in soluble form, the main culture is in most cases carried out at slightly lower temperatures (e.g., 22 or 28 ° C). Thus, inducible systems (e.g., with the trp, lac, tac or phoA promoters) as constitutive systems are suitable for the production of soluble proteins. After the late logarithmic phase (usually at an optical density of 0.5 to 1.0 in shake flasks) has been reached, an inducer (e.g., indolylacrylic acid, isopropyl-3-D-thiogalactopyranoside = IPTG) and incubation are added in inducible systems. continues for 1 to 5 hours. In this case, the inducer concentration is selected at the lower end to achieve moderate expression. During this time, most of the N ^pro -target protein fusion protein is formed, at the same time co-or post-translational cleavage of the N ^pro region occurs, so that at the end of culture in the culture system there are two cleavage regions separately. The cells may be harvested and further processed.

On a large scale, the multi-stage culture process takes place in a series of bioreactors (fermenters), with the use of defined nutrient media being preferred to improve process control and control. In addition, it is possible to significantly increase biomass growth and product formation by dosing certain nutrients (feed ration). Otherwise, the process is analogous to the small-scale process in shake flasks. So eg. For example, a pre-phase fermenter and a main phase fermenter are used and culture temperatures identical to those of the flask culture are selected. An inoculum that is grown from a single colony or cryoculture in a culture flask is inoculated into the pre-phase fermenter. It is also necessary to ensure good aeration and the presence of sufficient inducer concentration in the fermenter, especially in the main phase. However, the induction phase must sometimes be of a different length than the induction in the culture flask. The resulting cells are then used for further processing.

The heterologous target protein that has been cleaved from the fusion protein can be isolated by protein purification methods known to those skilled in the art (see, e.g., MP Deutscher, in: Methods in Enzymology: Guide to Protein Purification, Academic Press Inc., (1990), 309 - 392). The purification procedure usually comprises the steps of cell disruption, purification of the medium (by centrifugation or microfiltration), and then various chromatography, filtration and precipitation steps.

The following examples serve to illustrate the present invention without limiting its scope in any way.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

Expression and in vivo cleavage of the N ^pro -C fusion protein in a bacterial host

The plasmid NPC-pET was designed to express the N ^pro -C fusion protein in a bacterial host. The expression vector used was the pETIIa vector (FW Studier et al., Methods. Enzymol. 185 (1990), 60-89). The natural structural gene (from the RNA genome of CSFV) for the N ^pro -C fusion protein was cloned into this expression vector. The structural gene for the fusion protein was prepared by PCR amplification from a viral genome that was transcribed into cDNA (and cloned into a vector). Moreover, the first 16 amino acids of the natural N ^pro -sekvencie (MELNHFELLYKTSKQK) were replaced oligo-histidine tract 10 amino acids long, conducive purification (MASHHHHHHH). The resulting construct was designated NPC-pET. The N-region sequences ^{for the} autoproteolytic cleavage site of the N ^pro -C fusion protein encoded by NPC-pET have the following structure, where the cleavage site is located between amino acids Cysl68 and Ser (169):

MASHHHHHHHFVGVEEPVYDTAGRPLFGNPSEVHPQSTLKLPHDRGRGDIRTTLRDLPRKGDCR SGNHLGPVSGIYIKPGPVYYQDYTGPVYHRAPLEFFDEAQFCEVTKRIGRVTGSDGKLYHIYVC VDGCILLKLAKRGTPRTLKWIRNFTNCPLWVTSC (168) S (169) DDGAS- (nucleocapsid protein C).

In this sequence, proline 17 (position 2 of the fusion protein) from natural N ^{for the} sequences is indicated in italics and the beginning of the C sequence is marked in bold. The fusion protein has an M _{r of} about 32,000 (D), where after autoproteolytic cleavage, the N ^{pro region} corresponds to about 18,000 (D) and the C region corresponds to about 14,000 (D).

In order to assess the significance of the first amino acid C-terminally from the cleavage site, the naturally occurring serine 169 at this position was replaced sequentially by each of the 19 naturally occurring amino acids by targeted mutagenesis. The constructs thus prepared were designated as NPC-pET-Ala, NPC-pETGly, and so on. Expression strains were then prepared from these plasmids.

The Escherichia coli strain BL21 (DE3) was used as an Escherichia coli host strain to express the N fusion protein ^for -C. This strain had the following genotype:

E. coli ompT BF dem HSDS (r _b m _b) gal λ (ΌΕ3)

The strain was prepared from commercially available competent cells (Stratagene). It carries the lysogenic lambda phage, in the genome of which the T7 RNA polymerase gene is under the control of the lacUV5 promoter. The production of T7 RNA polymerase and thus of the target protein can be induced by isopropyl-1-D-thiogalactopyranosidone (IPTG). This biphasic system allows for highly specific and very high expression of many target proteins.

Expression strains BL21 (DE3) [MPC-pET], BL21 (DE3) [MPC-pET-Ala], etc. were prepared by transforming the respective expression plasmids into BL21 (DE3). Transformation was performed according to the instructions of the competent cell manufacturer (Stratagene or Novagen). The transformation mixture was plated on Luri agar plates containing 100 mg / l ampicillin. Transformation after incubation overnight at 37 ° C yielded several clones.

Medium sized colonies with distinguishable edges were picked and became the basis for the respective expression strains. Clones were cultured, and then preserved in cryo-vials at -80 ° C (master cell bank, MCB, master cell bank). For routine daily work, the strain was always plated on a Luri agar plate (containing ampicillin).

A single strain was used to inoculate the preculture in a shaking single flask culture flask on an agar plate. An aliquot of the preculture was used to inoculate the main culture (10 to 200 ml in a shaking culture flask) and was then cultured to an OD ₆₀ of 0.5 to 1.0. Fusion protein production was then induced with 1.0 mM IPTG (final concentration). Cultures were further cultured for 2 to 4 hours until a ₆₀ to 1.0 to 2.0 was achieved. The culture temperature was 30 ° C +/- 2 ° C and LB + 2 g / l glucose medium + 100 mg / l ampicillin was used.

Samples were taken from the cultures before induction and at various time intervals after induction, centrifuged, and the pellets were denatured by boiling in sample buffer and then analyzed by SDS-PAGE and Coomassie staining or Western blotting. Samples were taken under standardized conditions and the differences in culture density were compensated by the volume of loading buffer used to resuspend the sample.

Bands that appeared after induction were localized slightly above 20,000 (D) (corresponding to N ^pro ) and about 14,000 (D) (corresponding to C). Cleavage efficiency of the fusion protein in each construct was determined based on the intensity of the bands on a gel stained with Coomassie blue and then by Western blot. It was found that most amino acids were tolerated at the position immediately adjacent the C-terminal to the cleavage site (ie, at the N-terminus of the target protein), ie. that very efficient autoproteolytic cleavage has occurred.

These data show that the autoproteolytic activity of autoprotease N ^pro can in principle be successfully utilized to specifically cleave a recombinant fusion protein in a bacterial host cell.

Example 2

Expression and in vivo cleavage of fusion protein N ^pro and human interleukin 6 (hIL6) to produce homogeneous mature hIL6

NP6-pET plasmid was constructed for expression of a fusion protein ^of N -hIL6. PETIIa was used as the expression vector (FW Studier et al., Methods. Enzymol. 185 (1990), 60-89). First, a fusion protein consisting of N ^pro and CSFV nucleocapsid protein was cloned into the expression vector (see Example 1). The fusion protein structural gene was prepared by PCR. This made it possible to replace the first 16 amino acids of the natural N sequence ^for (MELNHFELLYKTSKQK) by 10 amino acids with a long oligo-histidine sequence (MASHHHHHHH) for purification.

The SpeI cleavage site was introduced into the resulting expression plasmid at the junction site between N ^pro and the nucleocapsid protein by site-directed mutagenesis. This allowed the deletion of the structural gene for the nucleocapsid protein from the vector by restriction of SpeI at the 5'-end (corresponding to the N-terminus of the protein) and XhoI at the 3'-end (corresponding to the C-terminus of the protein). The corresponding linearized vector N ^for -pET11a was separated from the nucleocapsid gene fragment by preparative gel electrophoresis. It was then possible to insert the structural gene hIL6 via the sticky ends of SpeI and XhoI.

The following preparatory work was necessary. The structural gene was amplified using a high-precision PCR system (for example, the Pwo system from Roche Biochemicals, following the manufacturer's instructions) of the hIL6 cDNA clone obtainable from C10-MJ2 cells. The following oligonucleotides were used for this purpose:

Oligonucleotide 1 (N-terminal):

5'-ATAATTACTA GTTGTGCTCC AGTACCTCCA GGTGAAG-3 '

Oligonucleotide 2 (C-terminal):

5'-ATAATTGGAT CCTCGAGTTA TTACATTTGC CGAAGAGCCC TCAGGC-3 '

Using these oligonucleotides, the SpeI cleavage site was introduced at the 5'-end and the Xho I cleavage site was introduced at the 3'-end. In addition, a ocher double stop codon (TAATAA) was inserted at the 3'-end of the structural gene for efficient translation termination. The SpeI cleavage site at the front end allows ligation in accordance with the reading frame of the vector N ^for -pET11a described above. The XhoI cleavage site at the rear end allows direct cloning.

The sequence of the PCR fragment (593 bp) with the structural gene hIL6 is shown below (read from the N-terminus to the C-terminus), with the restriction site underlined and the first codon hIL6 (Ala) and stop codon in bold:

ATAATTACTAGTTGTGCTCCAGTACCTCCAGGTGAAGATTCTAAAGATGTAGCCGCCCCACACA

GACAGCCACTCACCTCTTCAGAACGAATTGACAAACAAATTCGGTACATCCTCGACGGCATCTC

AGCCCTGAGAAAGGAGACATGTAACAAGAGTAACATGTGTGAAAGCAGCAAAGAGGCACTGG

CAGAAAACAACCTGAACCTTCCAAAGATGGCTGAAAAAGATGGATGCTTCCAATCTGGATTCA

ATGAGGAGACTTGCCTGGTAAAAATCATCACTGGTCTTTTGGAGTTTGAGGTATACCTAGAGTA

CCTCCAGAACAGATTTGAGAGTAGTGAGGAACAAGCCAGAGCTGTGCAGATGAGTACAAAAGT

CCTGATCCAGTTCCTGCAGAAAAAGGCAAAGAATCTAGATGCAATAACCACCCCTGACCCAAC

CACAAATGCCAGCCTGCTGACGAAGCTGCAGGCACAGAACCAGTGGCTGCAGGACATGACAAC

TCATCTCATTCTGCGCAGCTTTAAGGAGTTCCTGCAGTCCAGCCTGAGGGCTCTTCGGCAAATGT

AATAACTCGAGGATCCAATTAT

The construct prepared by ligation with plasmid N ^pro -pET11a was named NP6-pET.

The following is the N sequence ^{for the} -hIL6 fusion protein (347 amino acids of which 162 amino acids are N ^pro and 185 amino acids are hIL6), encoded by NP6-pET, with the hIL6 sequence in bold:

MASHHHHHHHPVGVEEPVYDTAGRPLFGNPSEVHPQSTLKLPHDRGRGDIRTTLRDLPRKGDCR

SGNHFGPVSGIYIKPGPVYYQDYTGPVYHRAPFEFFDEAQFCEVTKRIGRVTGSDGKFYHIYVC

VDGCIFFKFAKRGTPRTFKWIRNFTNCPFWVTSCAPVPPGEDSKDVAAPHRQPLTSSERIDKQI

RYILDGISALRKETCNKSNMCESSKEALAENNLNLPKMAEKDGCFQSGFNEETCLVKIITGLLE

FEVYLEYLQNRFESSEEQARAVQMSTKVLIQFLQKKAKNLDAITTPDPTTNASLLTKLQAQNQ

WLQDMTTHLILRSFKEFLQSSLRALRQM

The fusion protein has an M _{r of} 39,303.76 (D) in a reduced state, and after eventual cleavage of the N ^pro (reduced) region, the Mr 18 should be 338,34 (D) and the hIF6 (reduced) region would be 20,983.63 (D). . The N ^pro contains six cysteines and four hIF6. In the bacterial cytoplasm, these cysteines are likely to be mostly in reduced form. During further processing, at least a partial formation of disulfide bridges is likely to occur. It should be expected that the N-terminal methionine in the fusion protein (or part of the N ^pro ) is mostly cleaved by the host's own methionine aminopeptidase (MAP), which would reduce Mr by approximately 131 (D) to 39 172.76 (D) (fusion protein) and 18,207,113 (D) (N ^pro ).

The host strain of Escherichia coli for expression of the N fusion protein ^for -hIF6 is Escherichia coli BL21 (DE3) (see Example 1).

The BF21 (DE3) [MP6-pET] expression strain was prepared by transforming the already described expression plasmid MP6-pET into BF21 (DE3) as described in Example 1.

Strain BF21 (DE3) [MP6-pET] was inoculated from a single colony onto an agar plate, which was then used to inoculate precultures into FB medium (Furia Broth) containing 100 mg / l ampicillin (200 ml in a 1 l mixing flask with mixing flasks). ). The preculture was shaken at 250 rpm and 30 ° C for 14 hours until an OD ₆₀ of about 1.0 was reached. 10 ml aliquots of the pre-culture were used to inoculate the main culture (330 ml Luria Broth vill culture flask with mixing flasks) (3% inoculum). Main cultures were maintained at 30 ° C (250 rpm) until an OD ₆₀ of 0.8 was reached, and then fusion protein production was induced with 0.5 or 1.0 mM IPTG (final concentration). The cultures were further cultured at 30 ° C and 250 rpm for 3 hours, OD ₆₀ ° reaching about 1.0 to 2.0.

The cultures were then transferred to sterile 500 ml centrifuge tubes and centrifuged for 30 minutes at 10,000 g. The supernatant was completely removed and the pellets were frozen at -80 ° C until further processing.

The presence of new protein bands in the complete lysate was readily detected by Coomassie staining after SDS-PAGE. The bands in BL21 (DE3) [MP6-pET] lysate corresponded to an apparent molecular weight of approximately 19,000 (D), 21,000 (D), and 4,000 (D). Expression analyzes using anti-hIL6 antibodies basically confirmed Coomassie staining results.

To optimize N ^pro -hIL6 cleavage, induction was performed at various temperatures and IPTG concentrations and the resulting products were analyzed by gel staining and Western blotting. Nearly complete N cleavage ^for IL6 was observed when cultured at 22 ° C.

This experiment also showed that heterologous proteins can be fused to the C-terminus of the N ^pro in a bacterial expression system where very efficient cleavage occurs. Changing the N-terminal amino acid of the following protein (alanine instead of serine) also has no adverse effect. Thus, the system of the present invention is suitable for the production of recombinant proteins with a homogeneous authentic N terminus, especially in a heterologous expression system, such as e.g. a bacterial expression system, without the need for further processing steps.

Example 3

Expression and in vivo cleavage of a fusion protein consisting of N ^pro and human interferon α2B (IFNα2B) to produce homogeneous mature IFNα2B

The procedure for cloning IFNo2B until preparation of the NPI-pET vector corresponded to the procedure used for hIL6 in Example 2. The structural gene was amplified by high-precision PCR (for example, the Pwo system from Roche Biochemicals, following the manufacturer's instructions). The IFNo2B-cDNA clone was prepared from human leukocytes using standard procedures known to those skilled in the art. An alternative option would be to perform the synthesis of the complete gene. The structural gene sequence can be obtained electronically from the Genbank database under accession number V00548. The following oligonucleotides were used for amplification:

Oligonucleotide 1 (N-terminal):

5'-ATAATTACTA GTTGTTGTGA TCTGCCTCAA ACCCACAGCC-3 '

Oligonukieotide 2 (C-terminal):

5'-ATAATTGGAT CCTCGAGTTA TTATTCCTTA CTTCTTAAAC TTTCTTGCAA G-3 '

The sequence of the PCR fragment (533 bp) with the structural gene IFNo2B is shown below. Restriction enzyme cleavage sites are underlined and the first codon IFNo2B (Cys) and stop codon are in bold:

ATAATTACTAGTTGTTGTGATCTGCCTCAAACCCACAGCCTGGGTAGCAGGAGGACCTTGATGC

TCCTGGCACAGATGAGGAGAATCTCTCTTTTCTCCTGCTTGAAGGACAGACATGACTTTGGATT

TCCCCAGGAGGAGTTTGGCAACCAGTTCCAAAAGGCTGAAACCATCCCTGTCCTCCATGAGATG

ATCCAGCAGATCTTCAATCTCTTCAGCACAAAGGACTCATCTGCTGCTTGGGATGAGACCCTCC

TAGACAAATTCTACACTGAACTCTACCAGCAGCTGAATGACCTGGAAGCCTGTGTGATACAGGG

GGTGGGGGTGACAGAGACTCCCCTGATGAAGGAGGACTCCATTCTGGCTGTGAGGAAATACTT

CCAAAGAATCACTCTCTATCTGAAAGAGAAGAAATACAGCCCTTGTGCCTGGGAGGTTGTCAGA

GCAGAAATCATGAGATCTTTTTCTTTGTCAACAAACTTGCAAGAAAGTTTAAGAAGTAAGGAAT

AATAACTCGAGGATCCAATTAT

The construct prepared by ligation with plasmid N ^for -pET11a was designated NPI-pET.

The sequence of the N fusion protein ^for -IFNa2B (a total of 327 amino acids, of which 162 amino acids are N ^pro and 165 amino acids are IFNa2B) encoded by NPI-pET is shown below, with the IFNa2B sequence in bold (shown from N-terminal to C). apos; end):

MASHHHHHHHFVGVEEPVYDTAGRPLFGNPSEVHPQSTLKLPHDRGRGDIRTTLRDLPRKGDCRSG

NHLGPVSGIYIKPGPVYYQDYTGPVYHRAPLEFFDEAQFCEVTKRIGRVTGSDGKLYHIYVCVDGCI

LLKLAKRGTPRTLKWIRNFTNCPLWVTSCCDLPQTHSLGSRRTLMLLAQMRRISLFSCLKDRHD

FGFPQEEFGNQFQKAETIPVLHEMIQQIFNLFSTKDSSAAWDETLLDKFYTELYQQLNDLEAC

VIQGVGVTETPLMKEDSILAVRKYFQRITLYLKEKKYSPCAWEWRAEIMRSFSLSTNLQESLRS

KE

The fusion protein has an M _{r of} 37,591.44 (D) in a reduced state and after possible cleavage, the N ^for the (reduced) moiety would have Mr 18 338, 34 (D) and the IFNa2B moiety (reduced) would be 19,271.09 (D) . N ^pro has six cystine residues and IFNα2B has four. It is likely that these cysteine residues are largely in a reduced state in the bacterial cytoplasm. Disulfide bridges are likely to be formed at least partially during subsequent processing. It is necessary to take into account that the N-terminal methionine in the fusion protein (or in the N ^pro part) is mostly cleaved by the intrinsic methionine aminopeptidase (MAP), which would reduce Mr by 131 (D) to 37 460, 23 (D) (fusion) protein) and 18,207,13 (D) (N ^pro ).

The host strain of Escherichia coli for expression of the N fusion protein ^for -IFNa2B was Escherichia coli BL21 (DE3) (see Example 1).

The expression strain BL21 (DE3) [NPI-pET] was prepared by transforming the already described NPI-pET expression plasmid into BL21 (DE3) as described in Example 1.

The strain BL21 (DE3) [NPI-pET] was inoculated from a single colony onto an agar plate, which was then used to inoculate the precultures into LB medium (Luria Broth) containing 100 mg / l ampicillin (200 ml in a 1 L mixing flask culture flask). ). The preculture was shaken at 250 rpm and 30 ° C for 14 hours until it reached an OD ₆₀ of about 1.0. A 10 ml aliquot of the preculture was used to inoculate the main culture (330 ml Luria Broth vill culture flasks with mixing trays) (3% inoculum). Main cultures were maintained at 30 ° C (250 rpm) until an OD ₆₀ of 0.8 was reached, and then fusion protein production was induced with 0.5 or 1.0 mM IPTG (final concentration). The cultures were further cultured at 30 ° C and 250 rpm for 3 hours, OD ₆₀ ° reaching approximately 1.0 to 2.0.

The cultures were then transferred to sterile 500 ml centrifuge tubes and centrifuged for 30 minutes at 10,000 g. The supernatant was completely removed and the pellets were frozen at -80 ° C until further processing.

The appearance of new protein bands in the complete lysate was readily detected by Coomassie staining after SDS-PAGE. The bands in BL21 (DE3) [MP6-pET] lysate corresponded to apparent molecular weights of approximately 38,000 (D) and 19,000 (D). The IFNo2B band could not be separated from the N ^pro band by SDS-PAGE.

Expression analyzes using anti-IFNα2B antibodies confirmed the presence of the cleaved IFNα2B band.

To optimize cleavage of N ^cl ° -IFNoť2B also in this case, the induction performed at different temperatures and different concentrations of IPTG, and the resulting products were re-analyzed the stained gel and Western blotting. It was also found that complete cleavage occurred at reduced temperature (22-23 ° C).

Claims (13)

A vector for expressing heterologous proteins in a bacterial host cell comprising at least one expression control sequence and a nucleic acid molecule encoding a fusion protein, the fusion protein comprising a first polypeptide which is an autoprotease N ^for from pestivirus or a N-retaining derivative thereof ^for autoproteolytic activity, and comprising a second polypeptide which is a heterologous polypeptide, and wherein the second polypeptide is linked to the C-terminus of the first polypeptide in such a way that the first polypeptide can cleave the second polypeptide from the fusion and the cleaved second polypeptide has a clearly defined homogeneous N-terminus. The expression vector of claim 1, wherein the pestivirus is selected from the group consisting of CSFV, BDV and BVDV. The expression vector of claim 2, wherein the pestivirus is CSFV. 4. The expression vector of claim 3, wherein the first polypeptide comprises the following amino acid sequence: (I) -MELNHFELLYKTSKQKPVGVEEPVYDTAGRPLFGNPSEVHPQSTLKLPHDRGRGDIRTTL RDLPRKGDCRSGNHLGPVSGIYIKPGPVYYQDYTGPVYHRAPLEFFDEAQFCEVTKRIGRVTGS DGKLYHIYVCVDGCILLKLAKRGTPRTLKWIRNFTNCPLWVTSC- (168), or the amino acid sequence of a derivative-holding the autoproteolytic activity. The expression vector of claim 3, wherein the first polypeptide comprises the amino acid sequence Glu22 to Cys186 of autoprotease N ^pro for CSFV or a derivative thereof retaining autoproteolytic activity, wherein the first polypeptide additionally has a Met as the N-terminus, and wherein the heterologous polypeptide is linked directly to amino acid CysI68 of autoprotease N ^pro from CSFV. The expression vector of claim 3, wherein the first polypeptide comprises the amino acid sequence Prol7 to Cys186 of autoprotease N ^pro for CSFV or a derivative thereof retaining autoproteolytic activity, wherein the first polypeptide additionally has a Met as the N-terminus and wherein the heterologous polypeptide is bound directly to amino9 Cysl68 autoprotease N ^pro acid from CSFV. The expression vector of any one of claims 1 to 6, wherein the nucleic acid molecule is a DNA molecule. The expression vector of claim 1, wherein the bacterial host cell is an E. coli cell. 5 The expression vector of claims 1 or 8, wherein the expression vector is a plasmid. A bacterial host cell comprising the vector of any one of claims 1 to 9. The bacterial host cell of claim 10, wherein the host cell is an E. coli cell. A method of producing a desired heterologous polypeptide, comprising the steps of: (i) culturing a bacterial host cell according to claim 10 or 11, 10 performs under conditions that result in expression of the fusion protein and autoproteolytic cleavage of the heterologous polypeptide from the fusion protein in the host cell by the autoproteolytic activity of the first protein, and (ii) isolating the cleaved heterologous polypeptide. 15 End of document